Quick Answer: To string a grass trimmer, disconnect power, remove the spool from the trimmer head by unscrewing or pressing release tabs, remove old line, cut new line to the recommended length (typically 10–15 feet), insert one end into an anchor slot, wind the line tightly around the spool following directional arrows, secure the other end in its anchor slot, reassemble the head, and test the line feed.
Understanding Your Trimmer Head Type
Before you begin stringing your grass trimmer, you need to identify which spool mechanism your trimmer uses. Different designs require slightly different approaches, and attempting the wrong method can damage your spool or result in poor line feeding.
Common Trimmer Spool Types
Most residential grass trimmers use one of three spool designs:
- Bump Feed Spools: These manual-advance spools feed line when you tap the trimmer head on the ground. The spool remains stationary inside the head, and each tap advances pre-cut segments of line. This is the most common residential design and typically the easiest to restring.
- Fixed Spool Trimmers: The spool is permanently mounted and line is manually advanced by hand. Once line is exhausted, you remove the spool entirely to reload new line. This type offers the most control but requires more frequent maintenance on heavy-use trimmers.
- Automatic Feed Systems: These spools automatically extend line as it wears down during operation. Less common on basic models, they require careful line tension to prevent jams and waste.
Check your trimmer’s manual or look for directional markings and feed mechanism indicators on the spool itself. If you’ve lost the manual, the spool design is usually visible once you remove the trimmer head cover.
What You Need Before Starting
Gathering the right materials and tools prevents frustration and ensures a smooth restringing process.
Materials Required
- Trimmer Line (String): Purchase the correct gauge (thickness) for your trimmer model. Residential electric trimmers typically use 0.065 to 0.080-inch diameter line, while gas-powered or commercial models often require 0.095 to 0.105-inch line. Check your trimmer head or manual for the exact specification.
- Replacement Line: Buy pre-cut spools or bulk line. Pre-cut lengths are convenient but bulk line is more economical for frequent users.
Tools You May Need
- Screwdriver (usually Phillips head) or Allen wrench, depending on your trimmer model
- Needle-nose pliers for removing stubborn spools or old line remnants
- Scissors or utility knife for cutting new line to length
- Small brush or cloth for cleaning the spool and head interior
Determining the Correct Line Length
Line length varies by spool capacity. Most bump feed spools hold 10–15 feet of line, though larger commercial spools may accommodate 20+ feet. Check your manual or the spool itself for capacity markings. As a rule, cutting line slightly longer than recommended is better than too short—you can always adjust during winding. Line that’s too short may not load properly into anchor slots.
Step-by-Step: Preparing Your Trimmer
Safety First: Disconnect Power
Before opening the trimmer head, always disconnect the power source. For electric trimmers, unplug the cord or remove the battery. For gas-powered models, ensure the engine is cool and remove the spark plug wire to prevent accidental starting. This is non-negotiable—accidentally starting the trimmer during disassembly can cause serious injury.
Locate and Remove the Spool
The spool is housed inside the trimmer head, which is typically located at the bottom of the trimmer shaft. Depending on your model:
- Screw-On Heads: Rotate the entire head counterclockwise by hand or with a wrench until it separates. Some models have a small notch for a screwdriver to prevent rotation of the inner spool while you unscrew the head.
- Release Tab Heads: Look for one or two tabs on the side of the head. Press or pull these tabs while gently prying off the head cover. The spool may spring out slightly once the cover is released, so hold it steady.
- Bolt-On Heads: Remove bolts using the appropriate wrench or socket. Keep bolts organized so you don’t lose them during reassembly.
Remove Old Line and Clean the Spool
Once the spool is exposed, remove any remaining old line. Some line may be wound tightly; use needle-nose pliers to pull it free if it resists. Wipe the spool with a dry cloth to remove grass clippings, dirt, and debris. A clean spool ensures new line winds smoothly and prevents jams.
Measuring, Cutting, and Preparing New Line
Cut the Correct Length
Unroll your new trimmer line and measure the recommended length against a tape measure or by laying it against your spool’s marked capacity. For most residential bump feed spools, cut two segments of 5–7.5 feet each (totaling 10–15 feet). For fixed spools, refer to your manual for the exact length. Cut cleanly with scissors or a utility knife to create a straight edge—frayed or jagged ends are harder to load into anchor slots and may jam during winding.
Why Line Length Matters
Line that’s too short won’t wind properly around the spool and may slip out of anchor slots during operation. Line that’s too long creates excessive bulk, making it difficult to reassemble the head or wind tightly. The correct length ensures balanced tension and optimal line feeding.
Winding the Line: Step-by-Step Instructions
Universal Winding Method (Most Bump Feed and Fixed Spools)
Most residential trimmers follow this winding pattern:
- Locate the Anchor Slots: Your spool has two or more anchor slots around its perimeter—usually at the 3 o’clock and 9 o’clock positions for dual-line heads. These slots hold the line ends in place during winding.
- Insert the First End: Take one end of your cut line and insert it firmly into one anchor slot until it catches. The line should sit flush against the slot without protruding.
- Wind Tightly: Begin winding the line around the spool in the direction indicated by arrows embossed on the spool. Wind tightly and evenly, keeping slight tension on the line with your free hand. Loose winding causes poor line feed and tangling. Complete 5–8 wraps (depending on line length) before reaching the second anchor slot.
- Insert the Second End: Once you’ve wound most of the line, insert the remaining end into the second anchor slot. The line should be under tension—don’t allow slack to develop during this step.
- Verify the Wind: The wound line should lay flat and even across the spool with no overlapping or gaps. If you see crossing lines or bunching, unwind and start again; this causes jamming.
Winding Direction and Tension
Always wind in the direction indicated by arrows on the spool. Winding against the directional arrows prevents proper line advancement and can damage the feed mechanism. Maintain consistent, firm tension throughout winding—this is critical for automatic and bump feed systems that rely on tension to function correctly.
Special Instructions for Automatic Feed Spools
If your trimmer has an automatic feed spool, the winding method is identical, but pay extra attention to tension. Automatic spools are more sensitive to improper winding and over-tight line can cause binding. If your manual specifies a particular tension level, follow it precisely.
Reassembly and Testing
Reassemble the Trimmer Head
Once your line is wound and anchored:
- Align the spool with the head housing. The anchor slots should face outward, and any feed teeth or guides should align with grooves in the housing.
- Press the spool back into the head cover firmly until it seats completely. You should hear or feel a click if your model uses release tabs.
- Screw the head back onto the trimmer shaft, rotating clockwise by hand or with a wrench until tight. Don’t overtighten—this can strip the threads.
- Double-check that the head is secure and doesn’t wobble.
Test the Line Feed
Before full use, test your work:
- Reconnect power and hold the trimmer in a safe location away from people and objects.
- Gently tap the trimmer head on the ground (for bump feed models) to advance line. The line should extend smoothly without catching or bunching.
- For fixed spool models, manually check that line unwinds freely without resistance.
- Listen for unusual grinding or clicking sounds, which indicate a problem.
- If line doesn’t feed or jams immediately, stop and rewind.
Common Mistakes to Avoid
Winding Against the Directional Arrow
This is the most frequent error. Line wound backward won’t feed correctly and can jam or tangle immediately during use. Always verify the arrow direction before winding.
Loose or Uneven Winding
Slack in the wound line causes poor feed and tangling. Maintain constant tension and keep wraps flat and tight. If wraps cross over each other, unwind and start again.
Incorrect Line Gauge
Using thicker or thinner line than specified can damage the feed mechanism or prevent proper line advancement. Always check your manual for the exact gauge requirement.
Not Fully Seating the Spool
If the spool isn’t pressed completely into the head housing, line may not feed or the head may wobble during operation. Listen for a click or verify visually that the spool sits flush.
Skipping the Cleaning Step
Debris on the spool creates friction and jams. Always wipe the spool before winding new line.
Troubleshooting Common Issues
Line Doesn’t Feed or Feeds Sporadically
Causes: Anchor slots not fully seated, line wound too loosely, or debris in the feed mechanism. Solution: Remove the head, check that anchor ends are firmly in their slots, and verify winding tension. Clean the head interior thoroughly.
Line Breaks During Use
Causes: Improper line gauge for your model or line wound under excessive tension. Solution: Check that you’re using the correct gauge specification. If using the right gauge, slightly reduce winding tension on your next restring.
Line Tangles Inside the Head
Causes: Crossed or overlapping wraps, or winding against the directional arrow. Solution: Rewind carefully, keeping wraps flat and even. Verify the arrow direction.
Spool Won’t Reassemble
Causes: Line is too bulky or wound unevenly, or the spool isn’t aligned with the housing. Solution: Check that wraps are tight and flat. Verify that feed teeth or guides align with the head housing before pressing firmly.
Maintenance Tips for Long Spool Life
- Inspect Regularly: Before each use, check that line is intact and the spool head isn’t cracked or damaged.
- Store Properly: Keep your trimmer in a dry location. Excess moisture can cause line to swell or spool materials to warp.
- Avoid Striking Hard Objects: Hitting rocks, concrete, or metal objects dulls line and can damage the spool housing. Stick to grass and soft vegetation.
- Replace Line When Worn: Don’t wait until line breaks during use. Replace it when it becomes noticeably thin or frayed at the edges.
Frequently Asked Questions
How often should I replace my trimmer line?
Line lifespan depends on usage frequency and what you trim. Light residential use may only require line replacement every 2–3 months, while heavy use or striking objects frequently may require monthly replacement. Replace line whenever it becomes noticeably thin, frayed, or if the spool runs empty.
Can I use any brand of trimmer line on my trimmer?
No. You must use line that matches your trimmer’s specified gauge (diameter). Using incorrect gauge can damage the feed mechanism or prevent proper line advancement. However, many aftermarket brands work fine as long as they meet your trimmer’s gauge specification. Stick to reputable brands to avoid quality issues.
What’s the difference between 0.065-inch and 0.095-inch trimmer line?
The numbers refer to the line’s diameter. Thicker line (0.095-inch) cuts heavier vegetation and lasts longer but requires more power and creates more drag. Thinner line (0.065-inch) is ideal for delicate grass and light brush but wears out faster. Always use the gauge specified in your trimmer’s manual.
Why does my newly strung trimmer jam immediately?
The most common causes are winding against the directional arrow, loose or uneven winding, debris inside the head, or the spool not being fully seated. Remove the head, inspect the winding direction and tension, clean any debris, and verify the spool is flush in the housing. Rewind if necessary.
Can I leave a trimmer strung and ready to use, or should I remove the line when storing?
You can safely leave line on the spool during short-term storage (a few weeks). For long-term storage (several months), it’s best to remove old line to prevent it from drying out and becoming brittle. Before storing, clean the spool and head thoroughly to remove grass residue and moisture.
Final Tips for Success
Stringing a grass trimmer is straightforward once you understand your spool type and follow the directional winding pattern. Take time to verify the line gauge, cut the correct length, and maintain consistent tension while winding. If your first attempt doesn’t result in smooth line feeding, don’t hesitate to rewind—it takes only a few extra minutes and prevents frustration and damage. Most people successfully restring their trimmer in under 15 minutes once they’ve done it once.
